Steel reinforced concrete chimneys, television towers, bridge pillars and the like of substantial height have a variable cross-section for both static and economic reasons, i.e. the diameter or cross-section is tapered, usually the wall thickness decreasing with increasing height. The construction of such buildings may be accomplished by utilizing a sliding structure technique in which a lifting device serves to periodically hoist a supporting scaffolding, including a star beam system for the radial movement of yoke structures carrying sliding molds, a ring-shaped framework system tangentially arranged about the periphery of the building and working platforms connected to the supporting scaffolding.
With respect to buildings having variable cross-sections, the distances between the lifter units for lifting the sliding molds must be changed synchronously with respect to the wall inclination and wall thickness. The prior art devices for accomplishing this can be classified in two groups, those comprising a star beam system in which the radial movement of the yoke structures is guided by means of central symmetrical beams, and the ring-shaped system in which the adjustment of the radial movable yoke structures is performed by an annular framework. The framework is a lattice arrangement repeated in each support unit and tangentially connected along the periphery of the building in a ring-shaped arrangement. The ring-shaped construction may be enlarged or reduced with each lifting step by a mechanical system.
Due to increasing demands, namely, steel reinforced concrete chimneys to 300 meters in height and to 45 meters in diameter, the prior art heavy self-supporting latticed constructions for supporting the star beam system and associated heavy loads have become uneconomical. The supporting scaffolding is subject to cants, the climbing bars may become deformed and the concrete construction itself also suffers from deformation thus resulting in interruptions during the sliding operation. The same difficulties also arise with the framework system. Diagonal tensions on the winding tower, the ropes and the yoke structure increase as the total working platform area, the amount of concrete material and the number of people increases.
In both systems the configuration and arrangement of the yoke structure is an essential element. To date, the yoke structures have been rigid, rectangular frame structures, though in some cases one yoke post may be movable relative to the other. The inclination of the steel concrete walls to be erected has been achieved either by means of rigid, rectangular yoke structures with the steel molds maintained in a sloping position parallel to the wall inclination by means of spindles between the yoke post and the molds or in the ring-shaped system by means of spindles. In both systems, a uniform hoisting and reduction of the shell skin cannot be attained due to the arrangement of the yoke structures and the mold skin which cannot be adjusted synchronously. One side of the molds will always be pressed against the inclined concrete surface during the lifting operation. As a result, there is risk particularly with large diameters and a substantial inclination of the wall that concrete will be lifted with the sliding movement resulting in cracks being formed which may entail dismantling the building.
In the case of greater inclinations, it has been necessary to additionally incline the yoke posts of the support scaffoldings, and the guidance of the yoke posts has been insured by superimposed rolls. When the inclination was greater, jammings occurred because of the key effect, and the sliding movement was adversely affected.